Cultures of retinal pigment epithelium (PE) from newborn rats and from human eyes provide an opportunity to study these cells under controlled conditions. These cultures will be used to define the components of bovine serum that stimulate the phagocytosis of rod outer segments (ROS) by cultured normal rat PE and to study the role of these components in the phagocytic process. Beta-adrenergic agonists, which elevate cyclic AMP and reduce phagocytosis in cultured rat PE, will be applied to the basal or apical surface of rat PE grown on Millipore filters in order to localize beta-adrenergic receptor-linked adenylate cyclase. Concurrent measurements of the phagocytosis of ROS will help relate the site of cyclic AMP synthesis to the inhibition of phagocytosis by cyclic AMP. Presence of receptors on the basal surface would imply potential responsiveness by the PE cell to beta-adrenergic agonists present systemically, while the presence of apical receptors would raise the possibility that the PE could respond to intraocular beta-agonists from the retina. Properties of the PE that are involved in vitamin A metabolism will be measured in cultured human PE. The finding that a recently developed culture medium maintains retinyl ester synthetase activity in culture will be extended to the measurement of 11-cis-retinol oxidoreductase, cellular retinol- binding protein, and cellular retinaldehyde-binding protein to determine whether or not all of these properties are maintained. The effects of vitamin A and components of the culture medium on these properties will be explored. This work will provide a foundation for studying vitamin A metabolism in cultured PE and will advance our knowledge of the factors that influence the expression of vitamin A-related properties by the PE. These studies of the cell biology of normal PE will provide a basis for pursuing similar studies in eyes of animals and autopsy eyes of humans with hereditary retinal degenerations.